The present invention is directed toward reticles and methods of forming and employing the reticles.
Reticles are used in the semiconductor industry to form semiconductor devices having device features. There is a continuing effort to increase device density by scaling down device size, and state of the art devices currently have device features with dimensions well below one micron. Most reticles contain subarray areas containing the patterns for the memory features of the device. As the features size decreases, edge of array effects are observed. The edge of array effects are generally seen as critical dimension differences between the edge or corner of the subarray area and the subarray area a distance from the edge.
The edge of array effects may be caused by a number of factors. For example, process loading during the manufacture of a reticle may occur. Process loading during reticle manufacture may introduce error into the subarray area because the entire reticle pattern may contain dense and less dense or open areas. Similarly, process loading during wafer processing may occur that causes error to be introduced into the subarray area on the wafer. Stray light from less dense areas of a reticle can cause bulk exposure in a clear field reticle. Additionally, reticles may suffer from underexposure due to large dark areas of a dark field reticle to prevent underexposure.
The critical dimension difference has been addressed in a number of ways. For example, U.S. patent application Ser. No. 09/748,168 addresses the critical dimension difference by providing a process of manufacturing a photomask that includes forming a dummy pattern in less dense areas of the reticle and subsequently etching the dummy pattern away. The reticle provides improved critical dimension control. However, the reticle may not be easily inspected for defects and is process intensive.
Thus, there remains a need in the art for reticle patterns that address edge of array effects, and there remains a need in the art for methods of forming and using such reticle patterns.